Phase shifting is a reliable and widely used shape measurement technique. Because of its low cost, high speed, and precision, it has found applications in surgery, factory automation, performance capture, digitization of cultural heritage, and other applications.
Phase shifting belongs to a class of active stereo triangulation techniques. In these techniques, correspondence between camera and projector pixels is established by projecting coded intensity patterns on the scene. This correspondence can then be used to triangulate points in the scene to establish a shape of an object in the scene.
Like other active scene recovery techniques, phase shifting assumes that scene points are only directly illuminated by a single light source and thus that there is no global illumination. In practice, however, global illumination is ubiquitous due to inter-reflections and subsurface scattering. In fact, global illumination arises in virtually every real world scene. As a result, typical phase shifting produces erroneous results due to such global illumination.
Furthermore, phase shifting algorithms also typically assume that the light source is a perfect point with infinite depth of field. However, all sources of light have limited depths of field, which results in defocus. In order to account for defocus, existing phase shifting techniques need to capture a large number of input images.
Accordingly, new mechanisms for performing shape measurement are desirable.